Coral reefs thrive and provide maximal ecosystem services when they support a multi-level trophic structure and grow in favorable water quality conditions that include high light levels, rapid water flow, and low nutrient levels. Poor water quality and other anthropogenic stressors have caused coral mortality in recent decades, leading to trophic downgrading and the loss of biological complexity on many reefs. Solutions to reverse the causes of trophic downgrading remain elusive, in part because efforts to restore reefs are often attempted in the same diminished conditions that caused coral mortality in the first place. Coral Arks, positively buoyant, midwater structures, are designed to provide improved water quality conditions and supportive cryptic biodiversity for translocated and naturally recruited corals to assemble healthy reef mesocosms for use as long-term research platforms. Autonomous Reef Monitoring Structures (ARMS), passive settlement devices, are used to translocate the cryptic reef biodiversity to the Coral Arks, thereby providing a "boost" to natural recruitment and contributing ecological support to the coral health. We modeled and experimentally tested two designs of Arks to evaluate the drag characteristics of the structures and assess their long-term stability in the midwater based on their response to hydrodynamic forces. We then installed two designs of Arks structures at two Caribbean reef sites and measured several water quality metrics associated with the Arks environment over time. At deployment and 6 months after, the Coral Arks displayed enhanced metrics of reef function, including higher flow, light, and dissolved oxygen, higher survival of translocated corals, and reduced sedimentation and microbialization relative to nearby seafloor sites at the same depth. This method provides researchers with an adaptable, long-term platform for building reef communities where local water quality conditions can be adjusted by altering deployment parameters such as the depth and site.
Experimental data is presented comparing microbial fuel cell (MFC) power from buried (control) and chambered anodes exposed to slow flow pumping (2 mL/min). Results show that upon initial pumping (3 hrs), a robust upturn in MFC power from the chambered anodes was stimulated over several days, while a second pumping (4 hrs) appeared to resuscitate and sustain increased power for five more days. Analysis of energy gained (G) in the test setup vs. energy input (I) required for a commercial low power pump revealed a potential G/I ratio of 2.4. A pier side test was also conducted to demonstrate how tide-induced hydrostatic pressure changes could be used to pump an MFC chamber.
Power sources for marine systems are becoming more versatile, taking advantage several different electrochemical couples to provide energy in locations that are not serviced by conventional electrical loads. Renewable power from wind, solar, and tidal power continues to dominate power generation at the ocean surface. In sub-surface locations, primary batteries and sealed secondary battery systems are often used. More recently, microbial fuel cells are being testing to support undersea sensors and electronics. Both battery and fuel cell systems must take advantage of electrochemical differences in order to generate voltage and current. Typically, these systems operate with an oxygen reducing cathode that is paired with an oxidation reaction at the anode. Both aluminum and magnesium have been used in primary battery systems in underwater systems. Under standard conditions, theoretical cell voltages provided by aluminum and magnesium can be calculated to be 1.26V and 1.97V respectively (comparable to a typical alkaline battery cell at 1.5V). Similarly, theoretical voltages for sediment microbial fuel cells have been estimated on the order of 1V based on standard conditions. These theoretical voltages do not account for losses or differences due to environmental conditions, transport, electrodes, or cell design. Engineering these systems to minimize losses can focus on many different aspects of system design. We focus here on the cathode, in part because improvements in oxygen reduction could be applicable to both abiotic metal battery systems as well as the biological fuel cell system. Our approach here is to analyze the performance of the cathode using electrochemical and molecular biology techniques. Employing these techniques is important to obtain a more complete understanding of the cathode because of the typical biomass growth that must be accounted for on exposed electrode surfaces. In most prototype systems, cathode materials use inert materials such as carbon or stainless steel. In this study, we look at three common-place carbon materials, graphite plates, graphite fiber brushes, and carbon cloth, and their performance as cathode substrates in undersea power systems. A major driving force behind this study was the availability of these materials for large scale applications in the future. Additional consideration was given to past use in published field studies with primary batteries (aluminum, magnesium) or in microbial fuel cell systems. For this reason, we report here the performance of undersea cathodes through operation and electrochemical testing in a sediment microbial fuel cell system. The effect of oxygen concentration on performance was evaluated and a minimum dissolved oxygen concentration of about 3 mg/L was determined for proper function at cathodes. Electrochemical studies indicate two distinct processes taking place at the cathode surface. We also take an exploratory look at the microbial community supported on each of these materials. An examination of typical cathode microbial communities offers some mechanisms that could be used to improve abiotic cathodes through use of metal catalysts based on iron or manganese. Preliminary tests of manganese coatings indicated possible improvements in operating voltage and sustainable current density.
Abstract : U.S. Pacific Fleet (PACFLT) requires high-resolution topographic data of San Clemente Island (SCI) to support management of the islands natural resources and environment. Such a dataset will enable tracking of changes in erosion patterns, which may be precursors to training impacts on species and their habitats. In response to this need, this work effort generated several high-resolution, georeferenced aerial remote sensing data sets of SCI. This report describes the data deliverables and the analysis that has been done with them.
Abstract : Contaminants enter shallow coastal waters from many sources, including ships, shoreside facilities, municipal outfalls, spills, and nonpoint source runoff. Sediments are typically considered a primary sink for these contaminants. Sediments in many bays, harbors, and coastal waters used by the Department of Defense (DoD) are contaminated with potentially harmful metal and organic compounds. DoD is required by the Comprehensive Environmental Resource Conservation and Liability Act (CERCLA), as amended by the Superfund Amendment and Reauthorization Act (SARA) of 1986, to assess and if necessary remove and remediate these sites and discharges in order to protect the public health or welfare of the environment. To determine whether contaminants are moving into, out of, or remaining immobilized within the sediments, a determination of contaminant flux must be made. This project addresses the DoD/Navy requirement for compliance, cleanup assessment, and remediation decisions using an innovative technology to directly quantify the mobility and bioavailability of contaminants in marine sediments. The environmental risks posed by these contaminants are determined largely by the degree to which they remobilize into the environment. The project included demonstrations of the commercialized Benthic Flux Sampling Device (BFSD2) at sites in San Diego Bay (Paleta Creek) and Pearl Harbor (Middle Loch and Bishop Point). The demonstrations were used by evaluators from the CalEPA as part of their Technology Certification program process. The demonstrations were successful in showing accurate, precise, and repeatable results at both locations. The San Diego sites were used to emphasize repeatable performance, and the Pearl Harbor sites were used to emphasize the range of conditions for operation.
The objective of this project was to provide an assessment of sediment quality in the area of Naval Station San Diego (NAVSTA). The study focused on two issues: the characterization of sediments including contaminant levels, extent and related ecological consequences, and the evaluation of processes that control the levels, transport, and biological exposure of any potential contaminants of concern. Sediments were characterized based on a range of physical, chemical, and toxicological testing. Processes evaluated included contaminant sources, sediment transport, sediment-water exchange, and degradation. As part of the object, new technologies for assessment and remediation were demonstrated and validated alongside traditional methods.
